The invention relates to an arrangement for adjusting guide blades in a turbo-engine by means of the thermal expansion of an expansion rod acted upon by working gas, this expansion rod, at one end, being stationarily mounted to a supporting housing and, at its other end, being linked to the short lever arm of a step-up lever pivoted in the supporting housing.
It is known to let the adjustment of guide blades be controlled as a function of the temperature of the working gas, in which case an external control of the engine control unit may be superimposed on this control circuit. Adjusting arrangements of this type have become known, for example from U.S. Pat. Nos. 3,377,799, 3,628,329 or 4,391,093, in which a rod is axially movably arranged inside a perforated sleeve. In this case, working gas from the compressor flows around the sleeve so that, in the case of temperature changes, the sleeve first expands with respect to the internally extending rod. This expansion difference is used for adjusting the guide blades. After some time, the rod disposed in the interior of the perforated sleeve is also heated by the working gas flowing in by way of the bores so that the relative expansion between the rod and the sleeve becomes zero again. This adjustment is therefore suitable for controlling transient processes. According to these previously known arrangements, the transmission of the expansion difference to the guide blades takes place in that the arrangement is connected into the reaction circuit of a blade adjusting circuit. For this purpose, the arrangement is inserted into a wire cable control provided for determining the actual blade position and thus, when the adjusting arrangement is actuated, an intentional falsification is carried out of the actual-value transmitter for the control arrangement.
Based on this known arrangement, it is an object of the present invention to develop an adjusting arrangement of the above-mentioned type such that it permits a direct adjustment of the guide blades without the connecting of a separate control circuit.
According to the invention, this object is achieved by means of an arrangement wherein the expansion rod has a significantly different coefficient of linear expansion with respect to a supporting housing and wherein the step-up device is connected with a guide-blade-coupled adjusting ring.
The arrangement according to the invention has the significant advantage that a direct adjustment of the guide blades can be carried out without any connecting of an external control circuit. This results in shorter reaction times as well as in a reduced risk of system errors. The adjustment takes place strictly mechanically and is therefore advantageously independent of electric, hydraulic or other components. In addition, the arrangement distinguishes itself by its extremely simple construction.
As a result,
the number of parts, the manufacturing and logistics costs are drastically reduced; PA1 the assembly and the maintenance is shortened and simplified; PA1 the breakdown risk of electric, hydraulic components of the control circuit is eliminated and that of the mechanical components is minimized.
It is an additional advantage that the arrangement reacts without any problems and delays, for example, to load changes of the engine as a result of the fact that the working gas directly flows around it. Because of the direct mechanical transmission of the "differential expansion change=load change" signal to the adjusting guide blades, the known delays in the electric, hydraulic or other control elements of the control circuit are also eliminated.
Preferably, the long lever arm of the step-up device constructed as a step-up lever is connected with the control ring by way of a similarly linked connecting shaft, in which case the connecting shaft may be manufactured of the same material as the expansion rod and can therefore also function as an expansion rod. However, in this case, it does not have the same effect as the primary expansion rod because its change of length cannot be multiplied by the step-up factor of the step-up lever. In this case, it is possible to construct the step-up device as a one- or two-armed lever or as meshing toothed wheels.
The expansion rod preferably has reinforcing ribs for protecting against buckling, whereby, at the same time, its surface is enlarged and a faster heating and cooling can take place. Longitudinal reinforcing ribs of this type may also be mounted at the connecting shaft.
The step-up lever is preferably constructed to be one-armed and is radially aligned in the supporting housing or in the turbo-engine. In this case, the fulcrum of the step-up lever may be provided on the outside or on the inside, depending on which solution causes less weight or can be carried out more easily constructively.
For generating expansion differences, working gas flows around the expansion rod. Particularly suitable are spaces through which this working gas flows permanently, such as blowing-off spaces of compressors for cooling air or blocking air because short reaction times can be achieved as a result of the high heat transmission value of the flowing medium/expansion rod. It is also possible to provide suitable guide plates by means of which the air blown off the compressor is guided directly to the expansion rod, therefore also making it possible to advantageously shorten reaction times.
Another advantageous development of the invention provides that the arrangement is coupled with several adjusting rings of different compressors or compressor stages. This is possible because the adjustable guide blade stages which are situated behind one another generally must be adjusted in a synchronized manner if a displacement has occurred of the compressor working point. One possibility of coupling different adjusting rings consists of connecting these adjusting rings by way of a rotatable shaft, in which case this shaft may be linked either directly to the step-up lever or indirectly to the adjusting ring coupled to the step-up lever. An alternative coupling possibility consists of coupling several adjusting rings by way of a common push rod, an adapting lever having a defined transmission ratio of its lever arms being provided between each adjusting ring and the push rod. This makes it possible to control every guide blade stage corresponding to its individual flow data. It is also possible in this case to construct the shaft or the push rod to be bendable in order to be able to transmit the adjusting motion also in the case of unfavorable housing data.
For the functioning of the arrangement according to the invention, it is necessary that the expansion rod, or the connecting shaft, has a significantly different coefficient of thermal expansion than the surrounding supporting housing. In this case, the coefficient of thermal expansion of the expansion rod may be much larger or significantly smaller than that of the supporting housing. It was found that the ratio of the two coefficients of linear thermal expansion should be at least 2, in which case much higher values can be achieved by a suitable selection of material. Preferred materials for the supporting housing are, for example, X10, 17-4 PH which have an .alpha. of approximately 11.times.10.sup.-6 /K. A suitable material for the expansion rod is EPC10 or INCO 904 with an .alpha. of approximately 4.times.10.sup.-6 /K. It is also conceivable to manufacture the expansion rod from a fiber-reinforced ceramic material, since this material definitely has a low coefficient of thermal expansion of less than 4.times.10.sup.-6 /K.
Another advantageous development provides that the arrangement is arranged in the area of a high-pressure compressor and by way of a push rod or a shaft is coupled with adjusting rings of a low-pressure compressor. Thus, frequently only the front stages of a compressor, particularly the stages of a low-pressure compressor are equipped with adjustable guide blades while the last blade rows of a high-pressure compressor have only rigid guide blades. On the other hand, air is frequently branched off as blocking air or cooling air in the area of the last high-pressure compressor stages so that it is appropriate to arrange the adjusting arrangement according to the invention in the area of the high-pressure compressor.
The invention may be arranged within the framework of axial compressors, radial compressors or combined axial and radial compressors, in which case a coupling of the guide blades of the radial and the axial compressor also makes sense. It is also possible to use the invention within the framework of the turbine guide blade adjustment, in which case the expansion rod is preferably acted upon by working gas which is branched off behind the turbine stage.
In an embodiment of the invention, the step-up lever, with its fulcrum, is linked in the supporting housing, resulting in the thermally caused angle of rotation of the adjusting ring caused by the change of length of the expansion rod with respect to the supporting housing, multiplied by the step-up ratio of the step-up lever. An alternative construction of the invention provides that the step-up lever is linked directly to the adjusting ring, and two expansion rods are linked to it which are stationarily mounted at one end. Two expansion rods are therefore provided in this construction resulting in a larger angle of rotation of the adjusting ring with otherwise identical parameters. In this case, it is possible to manufacture both expansion rods with approximately the same coefficient of linear expansion; i.e., that both consist of the same material. In this case, the expansion rods will be arranged on both sides of the step-up lever. As an alternative, it is also possible to use two expansion rods with significantly different coefficients of linear expansion. In this case, both expansion rods will be arranged on the same side of the step-up lever.
Another advantageous development of the invention provides that the pivot of the stationarily linked end of the expansion rod can be displaced in the expansion direction relative to the supporting housing by means of an adjusting motor. This makes it possible to carry out a superimposing adjustment of the guide blades independently of the adjustment controlled by the temperature, for example, by way of the electronic engine control unit. It is also possible to construct the fulcrum of the step-up lever to be displaceable instead of changing the stationary pivot of the expansion rod. The adjusting motor in this case may be constructed to be hydraulic, pneumatic or electric.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.